In the atomization of fluids having strong nozzle-caking tendencies, such as fluids containing dissolved or suspended solids therein, the fluids are delivered by a nozzle having an exit orifice from which the fluid issues. The spray pattern from the exit orifice typically is such that a fraction of the fluid mass is caused to circulate, i.e., bend and reverse, immediately after leaving the exit orifice. This circulating flow causes the fluid to contact the downstream face of the nozzle causing the fraction to attach itself by surface tension or the like to such face. The fluid thereafter dries and the solids therein remain attached to the nozzle face in the form of a residue. This residue eventually builds up to such an extent that the exit orifice becomes completely or at least partially blocked, thereby impeding the proper fluid flow therethrough. This blocking action can occur even though a second atomizing fluid is used to shape or to enhance the atomization of the fluid containing the dissolved or suspended solids. As a result of such obstruction, fluid delivery through the nozzle must be halted periodically to remove the caked material so that proper delivery of the primary fluid can continue.
A typical fluid delivery environment in which the above problem becomes critical is in the handling of radioactive wastes containing dissolved or suspended radioactive solids in a slurry. Before disposal, such a fluid or slurry waste must be treated to remove the radioactive material therefrom. One way of treating the waste is to pass it through a calciner having a fluid bed comprised of heated, dried particles of the solids contained in the previous charges of the waste. The particles of the fluid bed are distributed substantially uniformly throughout the volume of the fluid bed and such particle distribution is essential to assure the proper formation and collection of subsequent particles from the calcined waste so that the particles can be removed from the fluid bed and directed to apparatus external to the calciner for further treatment.
The radioactive waste solution is directed at relatively high velocity into the calciner by a spray nozzle which is located above and in spaced relationship to or directly into the aforesaid fluid bed. The solids in such solution, when leaving the exit orifice of such a nozzle, have a tendency to circulate and thereby reverse in flow as described above, causing caking on the face of the nozzle at least adjacent to but more likely surrounding the exit orifice of the nozzle. Eventually, this caking obstructs the exit orifice to the extent that flow of the radioactive waste solution must be halted until the caked material is removed; otherwise, proper operation of the system cannot continue without sacrificing its yield.
Another disadvantage of using a spray nozzle with a calciner having a fluid bed is that the caked material could and often does get heavy enough near the face of the nozzle to cause the caked material to fall by gravity onto the fluid bed. The caked material, therefore, passes downwardly and through the fluid bed, thereby destroying its integrity and reducing its effectiveness for use in collecting particulate solids resulting from calcination.